Metal plating product and process

ABSTRACT

AN ALUMINUM ARTICLE MAY BE PROVIDED USING ELECTROPLATING WITH A CONTINUOUS, HARD, ABRASIVE RESISTANT SURFACE BY FIRST CLEANING THE ARTICLE AND ROUGHENING ITS SURFACE AND THEN PLASMA-PLATING THE ROUGHENED SURFACE WITH A METAL COMPATIBLE TO ELECTROPLATING. SUCH AS STAINLESS STEEL, AND COATING THE FINAL STEEL SURFACE WITH CHROMIUM USING THE CONVENTIONAL ELECTROPLATING TECHNIQUES TO PRODUCE THE   FINISHED PRODUCT. THE PRODUCT THUS CREATED CAN BE USED IN DYNAMIC SYSTEMS USING FAR LESS MOTIVE POWER AND LOWER BEARING LOADS THAN WOULD OTHERWISE BE REQUIRED WHEN USING ARTICLES MADE FROM CONVENTIONAL, HEAVIER FERROUS OR NON-FERROUS MATERIALS.

y 181, 1972 R. J. SPERL 3,677,908

METAL PLATING PRODUCT AND PROCESS Filed Nov. 12, 1970 2 Sheets-Sheet 1 j, Clean Surface Obz'azh \siailzless Sieel CoaiiggOn Sar' ace Using Zasma an Grind Stainless Sleel Surface Electra-Flake Ground Polish INEE'N T 01% Roberi J- Sperl BY ATTORNEYS July 18, 1972 'R. J. SPERL METAL PLATING PRODUCT AND PROCESS 2 Sheets-Sheet 2 Filed Nov. 12. L970 nvvzwme Robert Sperl ATTORNEYS United States Patent "ice 3,677,908 METAL PLATING PRODUCT AND PROCESS Robert J. Sperl, 2319 Pennsylvania Ave., Wilmington, Del. 19806 Filed Nov. 12, 1970, Ser. No. 88,936 Int. Cl. C23b 5/06, 5/48; C23c 11/00 US. Cl. 204-38 B 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION In manufacturing processes, particularly those involved in the handling of fabrics, filaments (synthetic and natural) and the like for the textile industry, it is necessary to use many pulleys, rollers, idlers, mandrels and the like. In those applications relating'particularly to the handling of threads and filaments it has been customary to chromium plate a steel roller. While generally satisfactory and having a low coefiicient of friction, as is required for such applications, such rolls are heavy and quite expensive, and the motive power requirements for driving the rolls are high. Accordingly, a great deal of money is spent on electric motors or other prime movers of suflicient horsepower to handle the loads. Hard coated aluminum textile rolls have been employed, but their coeflicients of friction are not as desirable as those of the chromium plated rollers. In the handling of textile filaments it is imperative to have a low coefficient of friction and as smooth a surface as possible to minimize wear and tear on the filaments and to prevent tracking or other than straightline movements of the filaments. Highly polished, hard chromium surfaces are greatly preferred in getting the desired results.

Recently it has become desirable to increase the speed of running filaments but very substantial obstacles are involved. The present moving elements are constructed of heavy steel and the motors driving these elements are generally operating at their top speeds. Thus, to get increased speeds one must replace the motors if one retains the present rollers and the like. This is an exceedingly expensive matter. Another approach is to use moving elements, such as rollers, constructed of a lighter metal. The most attractive cost-wise is aluminum. One can coat aluminum surfaces using hard materials but the final product is not always desirable in the textile industry because the coelficient of friction is not acceptable and because the filaments do not run as well as they do on chromium. It is possible to apply chromium metal by the plasma system directly to aluminum surfaces but the hardness is only one-third that of electroplated chromium. The coating obtained by the plasma technique is a soft chromium and is easily dented or bruised. For example, the Brinell Hardness is about 500 or less whereas that of electroplated chromium is 1000 or more. Further, it is relatively difiicult and time consuming to plate aluminum.

3,677,908 Patented July 18, 1972 Some of the difficulties encountered in electroplating aluminum and aluminum alloys is set forth in some detail in ASTM Specification B 253-53 entitled Preparation of and Electroplating on Aluminum Alloys. As noted therein, these difficulties arise because the diiferent aluminum alloys behave differently electro-chemically since they have different metallurgical structures and, in addition, aluminum products tend to have a natural oxide film which is difficult at best to remove to provide a suitable surface for plating, resulting in poor adhesion of the plated metal.

Accordingly, it is an object of this invention to obviate many of the disadvantages of the prior art metal plated aluminum articles. Another object of this invention is to obviate many of the problems inherent in plating articles. Still another object of this invention is to provide an improved metal plated article. A further object of this invention is to provide an improved process for manufacturing plated articles. A still further goal is the provision of light weight rotatable elements made of aluminum but which have outer, highly polished smooth and very hard chromium surfaces. These objectives, among others, will be seen hereinafter.

BRIEF DESCRIPTION OF THE INVENTION According to the process of this invention, an article to be coated with a metal is severely cleaned with a solvent to remove grease and then its surface is roughened with a grit blast of known type. The article thus surface cleaned and roughened is then plasma-plated with a first metal that is capable of adhering and filling any pits or undesired cavities, dents or other depressions in the surface of the article. Next, a desired finish or second metal is electroplated over the first metal thereby to establish the desired finish coating over the article with the coating having the desired adhesion.

In a preferred embodiment of the invention, an aluminum article is coated by plasma-plating with stainless steel and the stainless steel coat is in turn electroplated with chromium which has a hard finish and is abrasive resistant with excellent adhesion. During the plasma-plating operation the article being coated is generally cooled using any conventional means.

The resulting product is thus seen to have a base material, as, for example, of aluminum, with a layered coating of a relatively hard metal thereover which has the' capability of filling up any pits, depressions and the like in the surface of the article. This coating having been applied by plasma-plating adheres very well and provides a good, hard base upon which the last layer, preferably of chromium, is deposited by electroplating. This third or finish layer, after grinding and polishing, provides a hard coating that presents a very low friction to textile materials and hence the coated element is suitable for use in textile rolls, mandrels and the like. These are advantageously light weight and require a low driving power. The surface is very smooth and abrasion resistant and has a low coeflicient of friction. Further, the process permits damaged, electroplated rolls, mandrels and the like to be repaired without distortion. Rolls and mandrels previously though to be scrap because of deep dents, etc., in the surfaces can be salvaged by plasma coating with suitable materials and subsequently electroplating.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its apparatus and method, as well as additional objects and advantages thereof, will best be understood from the fol- 3 lowing description when read in connection with the accompanying drawings, in which:

FIG. 1 is a'block diagram setting forth the steps of the process of this invention;

FIG. 2 is a side elevation view, partially cut away, i1- lustrating a typical article formed by the process of this invention;

FIG. 3 is an end elevation view of the article of FIG. 2 depicting the plasma-plated and electroplated layers forming the exterior surface;

FIG. 4 is a plan view of a jig adapted to complete the plasma-plating step of the process of this invention;

FIG. 5 is an end cross-sectional view taken on line 5-5 of the jig of FIG. 4 with the workpiece in plasmaplating position; and

FIG. 6 is a cross-sectional view of electroplating apparatus for effecting the electroplating step of the process of this invention.

DETAILED DESCRIPTION OF THIS INVENTION Although the process of this invention has many other applications, it will be described in conjunction with the manufacture of and/or repair of a damaged roll of the type typically used in the textile industry for the guiding of threads or filaments. The roll 10 itself, as typically used in this industry, has a tubular skeleton 11 formed of steel, both ends of which are bored as at 16 and then counterbored as at 17 so as to form a truncated interior tubular center section 18 in which spindles may be used for mounting and driving the roll. However, for the purpose of this invention the roll 10 is constructed of aluminum.

The skeleton, aluminum roll 11 is placed in a jig 12 (FIGS. 4 and 5) and severely cleaned first with a suitable solvent to remove all grease, dirt and the like. Next, the degreased skeleton roll 11 is grit blasted with sand, aluminum oxide or other suitable abrasive material sufficiently to roughen the surface. The function of the jig 12 is to hold the skeleton roll 11 in place and rotate it as by drive motor 14 while it is being processed. End caps 20 may be placed over either end of the tube to position it in the jig, and suitable glands in the end cap may seal the interior of the hollow skeleton roll such that a cooling fluid such as air, water, liquid carbon dioxide, liquid nitrogen or any other non-contaminating cooling fluid 38 may be passed therethrough to maintain the skeleton roll 11 relatively cool during subsequent processing. By use of the cooling procedures one can plasma-coat plastic articles with any of the various metals normally used in plasma-coating procedures in spite of the high temperatures involved. Synthetic organic polymeric and natural occurring organic polymeric materials which can be treated in accordance with the process of this invention to produce light weight useful articles such as rolls, plates, mandrels, sheets and the like include polyamide, polyurethanes, poly(tetrafluoroethylene), polyacrylics and meth- -acrylics, rubber, synthetic rubbers of all kinds, among many others. It is also to be appreciated that the base member that is plasma-coated can again be plasma-coated with a material different than that first applied. Such articles alford advantages in the field of corrosion resistant articles and in the heat transfer field.

Next, in accordance with the process of this invention, the skeleton roll 11 is plasma-plated with stainless steel utilizing a plasma gun 22 of conventional design which is available commercially, having a power supply 23. Plasma-plating as is known may be accomplished in several Ways. The most frequently used includes passing an inert gas, such as argon, through an electric arc. The gas molecules are then split into atoms and decomposed into ions which constitute the plasma. The plasma is then accelerated to sonic velocity and has intense heat (l5,000 to 30,000 E). The powdered metal supplied from a source 28 is fed into the plasma stream and is jetted as melted particles from a nozzle as a high velocity plasma jet. The melted material is deposited on the exterior of the skeleton roll 11 with excellent penetration and adhesion to the roll. The said roll 11 is turned at a constant rate, preferably in the order to 75 revolutions per minute (r.p.m.) while the plasma gun 24 traverses back and forth along the axis of the roll 11. The cooling fluids circulated through the skeletal roll 11 by a pump 29 maintain the metal of the roll itself at a temperature typically less than 400 F. The plasma gun 22 may be mounted on a reversing traverse screw 24 and guide rod 26 such that When the screw 24 is rotated by a motor 28, the gun 22 accomplishes the back and forth traversals along the axis of the roll 11 while the roll 11 itself is rotated by the motor 14. Alternatively, the plasma-plating may be accomplished by hand manipulating the gun which is often desirable while filling up its pits, dents and the like in the roll surface.

The coating metal employed in the plasma gun may be any hard material compatible with chrome plating, such as stainless steel, copper, nickel, Nichrome and the like. Generally a coating thickness 34 (FIG. 5) somewhere in excess of 2 mils and less than 7 mils is made. The coating is then usually ground back to a lesser thickness (not less than .002 inch in order to avoid porosity of the skeletal base material) to obtain a smooth surface. This grinding step is not essential for effecting the electroplating and may be and is, in fact, omitted in certain instances. For example, if one desires a mat finish in the final surface, there is no need to grind before electroplating.

Next, the stainless steel coated roll 42 is placed in an electroplating bath FIG. 6 and plated with hard metal. In a preferred embodiment, chromium is the plating metal, since it is hard, abrasion resistant and has a low co-efiicient of surface friction. The ends of the roll 42 (FIG. 6) are protected by conventional methods such as lacquer and the like or capping with a polymeric, acid resistant closure during electroplating. The electroplating bath may include, as seen in FIG. 6, a vessel 30 having the stainless steel coated roll 42 attached to one electrode, and a piece of lead 32 to the other. Both the plasma-coated skeletal roll 42 and the lead piece 32 are immersed in a suitable chemical solution to effect the plating operation. After the electro-plating is finished in the usual fashion to apply a chromium plate of about 0.008 inch, this surface is ground and polished in the usual manner to produce highly smooth surfaces having low co-efiicients of friction. The plasma-coating of stainless steel has an adhesion of at least about 3,000 psi. and that of the chromium is at least that high or higher.

When the intermediate layer 34 (FIG. 3) is stainless steel and the exterior layer 36 is chromium, in accordance with the preferred embodiment of this invention, the resulting roll as seen in FIGS. 2 and 3, is one in which the dents, pits, etc. have been completely filled in to permit a very smooth chromium coating. Both coatings have excellent adhesion and, since the chromium adheres to the stainless steel very strongly, there is little chance of peeling and he like with use. The final product is lighter than those achievable using a stainless steel roll and can be produced for relatively small additional expenditure. The resulting lighter product permits he use of lower horsepower drive motors and decreases the wear and tear on the mounting bearings, etc. For example, by use of chromium plated aluminum rolls it is possible to efiect a weight reduction of about 35%. A more substantial economy is elfected while allowing very substantial increases in the speed of production while retaaining the advantages of a hard, abrasion resistant coating of low co-efiicient of friction with excellent adhesion.

As one example of a particular process used to produce the product of this invention, the plasma-plating is done utilizing a stainless steel alloy bearing the designation 420SS having a Rockwell hardness of 28 and a high chromium content, which is available from Avco Corporation. The plasma-plating is done at a relatively low rate to avoid porosity of the resulting product, i.e., 10 grams per minute are overspread on the surface. The stainless steel is powdered. The plasma-plating is then performed until a plating layer of 0.014 inch is achieved. This layer is then ground back using conventional grinding techniques to a thickness of .007 inch. Thus prepared the plated roll is then placed in an electroplating bath and coated with chromium to the desired thickness which may then be ground and lapped as desired to provide the desired smothness. In this connection it may be noted that the electroplated result provides a far smoother layer, i.e., 2 RMS typically, whereas the best that can be achieved using direct plasma coating ois 8 RMS. The resulting chromium plated roll 10 (FIG. 2) with the underlying layer of stainless steel 34 is a relatively hard roll having a Brinnell Hardness of 1,000 or more. This compares very favorably to chromium layers that are deposited directely by plasma-plating in which Brinnell Hardnesses of only 500 or less can be achieved.

It is also possible to use base members that are of metals other than aluminum. For example, one can plasma-coat articles made of magnesium alloys or titanium alloys with stainless steel and then chrome-plate as described. Both these materials, like aluminum, cannot be readily chromeplated directly.

It is intended to cover such modifications and changes as would occur to those skilled in the art, as far as the following claims permit and as far as consistent with the state of the prior art.

What is claimed is:

1. A metal product having a hard, abrasion resistant coating of low co-eflicient of friction, said product comprising:

a base member,

a plasma-coating of a metal deposited on the exterior of said base member, and

an outer electroplated coating of a metal deposited on said plasma-coating.

2. A product according to claim 1 wherein said base member is made of aluminum, thereby to reduce the weight of said product.

3. A product according to claim 1 wherein said base member is made of an organic polymeric material.

4. A product according to claim 1 wherein said plasmacoated metal is stainless steel thereby to improve the strength of said product with adhesion of about 3,000 p.s.i.

5. A product according to claim 1 wherein said electro-plated metal is chromium, thereby to aiford a surface having a low co-efiicient of friction and having a Brinnell Hardness of at least 1,000.

6. A product according to claim 1 wherein said plasmacoated metal is a high chromium content stainless steel having a Rockwell Hardness of 28 or more.

References Cited UNITED STATES PATENTS 2,957,782 10/1960 Boiler 29-197 X 3,210,840 10/1965 Ulam 29-196.2 X 3,355,265 11/1967 Hudson et a1. 29-1962 X 3,496,621 2/1970 Winter 29-1962 X F. C. EDMUNDSON, Primary Examiner US. Cl. X.R. 

